Greetings,
Can you please share what ports the EVO's are connected to.... and the BIOS settings for for RAID Mode you are using?
Windows 7 - no native xHCI support in pre-boot environment
Windows 8 - has it
Default BIOS settings usually handle windows 7 USB support in preboot. If you've changed them, Load Set Up Defaults and configure your RAID again, ensuring the ports match what the BIOS is expecting. Also.... ensure you have entered the RAID Config Utility (ctrl+F) and marked the EVO's as member disks for RAID 0 or 1 whichever you are using. Reviewing pages 28~31 in your manual may be helpful. I hardly (RTFM) either

If there's more to the story... like UEFI boot, please share.